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ftrace: Do not blindly read the ip address in ftrace_bug()
It was reported that a bug on arm64 caused a bad ip address to be used for
updating into a nop in ftrace_init(), but the error path (rightfully)
returned -EINVAL and not -EFAULT, as the bug caused more than one error to
occur. But because -EINVAL was returned, the ftrace_bug() tried to report
what was at the location of the ip address, and read it directly. This
caused the machine to panic, as the ip was not pointing to a valid memory
address.
Instead, read the ip address with copy_from_kernel_nofault() to safely
access the memory, and if it faults, report that the address faulted,
otherwise report what was in that location.
Link: https://lore.kernel.org/lkml/20210607032329.28671-1-mark-pk.tsai@mediatek.com/
Cc: stable@vger.kernel.org
Fixes: 05736a427f
("ftrace: warn on failure to disable mcount callers")
Reported-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Tested-by: Mark-PK Tsai <mark-pk.tsai@mediatek.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
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@ -1967,12 +1967,18 @@ static int ftrace_hash_ipmodify_update(struct ftrace_ops *ops,
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static void print_ip_ins(const char *fmt, const unsigned char *p)
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{
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char ins[MCOUNT_INSN_SIZE];
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int i;
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if (copy_from_kernel_nofault(ins, p, MCOUNT_INSN_SIZE)) {
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printk(KERN_CONT "%s[FAULT] %px\n", fmt, p);
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return;
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}
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printk(KERN_CONT "%s", fmt);
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for (i = 0; i < MCOUNT_INSN_SIZE; i++)
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printk(KERN_CONT "%s%02x", i ? ":" : "", p[i]);
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printk(KERN_CONT "%s%02x", i ? ":" : "", ins[i]);
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}
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enum ftrace_bug_type ftrace_bug_type;
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